If you have the original battery Reserve Capacity specs it is an acceptable quick test to see if the battery is good but maybe worn or at end of life.
If possible test the battery(s) individually, Charge fully, bring battery to around 80F and time how long it will sustain a 25 amp load before reaching 10.5v. Note that takes the battery to almost complete discharge and may significantly shorten it's life. If the voltage gets to 11.0v and the time is less than half the RC spec there is not much to be gained testing further, the battery is worn out. The 10.5v sounds pretty bad but that is an under load voltage and is different from an at rest voltage. Michael Brown Windburn C&C 30-1
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